Motown legend Smokey Robinson has filed a $500m (£370m) defamation lawsuit against four former housekeepers who have accused the singer of sexual assault.

The legal case filed by the star and his wife Frances on Wednesday in California accused the women of fabricating the sexual assault allegations as part of an "extortionate" lawsuit.

The Robinsons say the alleged victims, who filed their case anonomously, went on family holidays with the couple and celebrated holidays together.

The singer, who is now also under criminal investigation in Los Angeles over accusations of sexual assault, has denied all the allegations, and his lawyer said those behind the accusations were after his money.

Mr Robinson's lawyers also filed a motion to dismiss the women's lawsuit, arguing they should not have been granted anonymity.

"The Robinsons did not abuse, harm, or take advantage of plaintiffs; they treated plaintiffs with the utmost kindness and generosity," the lawsuit states.

The women filed the lawsuit in Los Angeles Superior Court on 6 May under the pseudonyms Jane Doe 1, 2, 3 and 4.

In the 27-page legal action, they alleged several incidents that they said dated back to 2006, and accused Mr Robinson of pressuring them into sex.

All four women, who are of Hispanic descent, said they had not come forward until now because they feared losing their livelihoods, familial reprisal or embarrassment. Some were concerned the allegations could affect their immigration status.

They are seeking at least $50m (£38m) in damages and a jury trial.

The Los Angeles County Sheriff's Department then opened its investigation, which the 85-year-old singer said at the time he welcomed "because exposure to the truth is a powerful thing".

Mr Robinson was Motown's first hitmaker, writing number one records like Mary Wells' My Guy and The Temptations' My Girl.

He was both a talent scout for the record label and one of its most prominent recording artists in his own right, known for songs like Tracks of My Tears, Shop Around and Tears of a Clown.

He has spots in both the Rock & Roll Hall of Fame and the Songwriters Hall of Fame, and claims to have credits on more than 4,000 songs.